Its obvious that having children must be a positive biological function that prior generations somehow wanted to do, or we wouldn't be here. Any species that doesn't breed goes extinct. So I believe these factors are the root cause of why children suddenly seem like such a "problem":

1. Lack of support network -- many people living as just a couple or alone (and the strain on couple is so high that likely they will be alone soon).

2. Social emphasis on individualism rather than self-sacrifice or community focus.

3. Breakdown of community and trust -- so watching and keeping kids safe is full time job. Must be driven to and from everything, no playing by themselves after school.

4. Increased education -- older parents with more debt and pressure, working in more demanding and/or rewarding jobs.

5. Children need more -- expense of having child keeps increasing. The cost of all goods rising relative to wages, but also the cost of school, daycare, extra-curriculars, etc. Basically having a child is a huge cost, the medical bill just to have the child can be $20K in some hospitals. In most of the world that would mean no one could have a child in a hospital.